Predicting low density polyethylene melt rheology in elongational and shear flows with “pom-pom” constitutive equations

Inkson, Nathanael; McLeish, Tom; Harlen, Oliver G.; Groves, D. J.

doi:10.1122/1.551036

Cited by 210 publications

(159 citation statements)

References 37 publications

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“…Moreover, the MWD is very broad in this type of polymer. Yet melt rheology has been successfully predicted using constitutive equations based on molecular considerations [163,164]. The 'pom-pom' molecular model (see Fig.…”

Section: State-of-the-artmentioning

confidence: 99%

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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Abstract:The aim of this review is to provide evidence that rheological testing is a potent tool for characterising polymers in the melt. An effort has been made in order to gather results in conventional and model polyolefins, and correlating them with phenomena occurring at the molecular level. We have focused our interest on long chain branching (LCB). In the case of materials containing long side-chain branches, strong effects on viscosity, elastic character and activation energy of flow are general features. Literature results mostly indicate that the effect of polydispersity on these parameters could be very similar to that expected due to the presence of LCB -notwithstanding that the effects of LCB seem to be stronger than those due to polydispersity for a given molecular weight. Different relaxation processes appear as a consequence of the presence of LCB: slower terminal relaxation behaviour than of linear counterparts, and faster additional branch relaxation at higher frequencies, clearly distinguishable from polydispersity effects. To measure the amount of LCB from limited viscoelastic data and molecular properties seems to be a suitable instrument to explain the rheological features of the different polymers, but it fails when the results are compared with measured values of LCB density in model polymers. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the polymer main chain are the main factors that control the rheology of the material.

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Section: State-of-the-artmentioning

confidence: 99%

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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“…Recently, a polydisperse version of the theory has been used to account quantitatively for a very wide set of nonlinear rheological data on a standard LDPE. 15,16 To achieve this, it was necessary to invoke a physical consequence of the tube model around the branch points themselves. Termed "branch point withdrawal", it describes the shift of a branch point within a LCB polymer under strain toward the tube containing the strand of greatest tension meeting at the branch point.…”

Section: Introductionmentioning

confidence: 99%

“…S RPA (q) ) S 0 AA (q‚E) S 0 BB (q‚E) -S 0 AB (q‚E) 2 S 0 AA (q‚E) + S 0 BB (q‚E) + 2S 0 AB (q‚E) (15) …”

mentioning

confidence: 99%

Arm Relaxation in Deformed H-Polymers in Elongational Flow by SANS

Heinrich¹,

Pyckhout‐Hintzen²,

Allgaier³

et al. 2002

Macromolecules

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We present a small-angle neutron scattering (SANS) investigation of the relaxation process of branched polymer melts under deformation. The selected model polymer is an H-shaped polyisoprene having deuterium-labeled blocks at the dangling tips of the arms. The melt is step strained in a strain rig especially built for that purpose, where the sample temperature and its deformation conditions are precisely controlled. Uniaxial extensions to values of 2 and 3 are performed at a temperature above the polymer glass transition temperature T g. The sample is then allowed to relax during a given time before being quenched to below its Tg in order to freeze the chains conformation to perform the SANS experiments. Very large anisotropies in S(q) develop on time scales corresponding to the relaxation of the dangling arms. The experimental structure function is then compared to theoretical ones obtained by the random phase approximation applied to the tube model. While theory describes well the scattering for short times, it seems not to be able to describe the increase of intensity in the direction parallel to the strain at higher times, even when highly nonaffine processes such as arm retraction and branch point withdrawal are taken into account.

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“…Constitutive equations of the differential type have been used to model rheology of such complex topologies in different types of deformations (see [21][22][23]). Pivokonsky et al [1] presented experimental data in shear and elongation of two highly branched film-blowing grades of LDPE, and analyzed their data successfully by use of three different advanced differential constitutive equations, the so-called XPP model, the PTT-XPP model and the modified Leonov model.…”

Section: Introductionmentioning

confidence: 99%

Rheological Characterization and Constitutive Modeling of Two LDPE Melts

Rolón-Garrido¹,

Pivokonský²,

Filip³

et al. 2009

AIP Conference Proceedings

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Abstract. Experimental data of two low-density polyethylene (LDPE) melts at 200°C for both shear flow (transient and steady shear viscosity as well as steady first normal stress coefficient) and elongational flow (transient and steady-state elongational viscosity) as published by Pivokonsky et al. [1] were analyzed by use of the Molecular Stress Function (MSF) model for broadly distributed, randomly branched molecular structures. For quantitative modeling of melt rheology in both types of flow and in a very wide range of deformation rates, only three nonlinear viscoelastic material parameters are needed: While the rotational parameter, 2 a , and the structural parameter, E , are found to be equal for the two melts considered, the melts differ in the parameter 2 max f describing maximum stretch of the polymer chains.

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Predicting low density polyethylene melt rheology in elongational and shear flows with “pom-pom” constitutive equations

Cited by 210 publications

References 37 publications

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Arm Relaxation in Deformed H-Polymers in Elongational Flow by SANS

Rheological Characterization and Constitutive Modeling of Two LDPE Melts

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